Method for processing workpieces by ultrasonic energy

Abstract

A method of welding two thermoplastic workpieces (W) together along a predetermined weld line during a weld cycle utilizing a high frequency vibration sonic or ultrasonic welding apparatus. This welding apparatus includes an electroacoustic transducer (18) which transmits such vibrations to a horn (19) which is dimensioned to be resonant with the horn being brought into forced engagement with at least one of the workpieces to be welded. The method comprising the steps of bringing the workpieces into bearing relation against one another along the weld line. Then the electroacoustic transducer is energized so as to resonate the horn with a desired motional amplitude. Forceful contact is established between the horn and one of the workpieces. Then, the forceful contact between the horn and the one workpiece is maintained throughout the weld cycle. The motional amplitude of the horn is varied in accordance with a desired motional amplitude profile.

What is claimed is: 
     
       1. A method of operating on a thermoplastic workpiece during a work cycle utilizing a high frequency vibration sonic or ultrasonic apparatus, said apparatus comprising an electroacoustic transducer which transmits such vibrations to a horn which is dimensioned to be resonant and which is in forced engagement with the workpiece to be processed, said method comprising the steps of: establishing forceful contact between said horn and workpiece;   energizing said electroacoustic transducer so as to resonate said horn with a desired motional amplitude;   maintaining said forceful contact between said horn and said workpiece throughout said work cycle; and   varying said motional amplitude of said horn in accordance with a desired motional amplitude profile.   
     
     
       2. A method of welding two thermoplastic workpieces together during a weld cycle utilizing a high frequency vibration sonic or ultrasonic apparatus, said apparatus comprising an electroacoustic transducer which transmits such vibrations to a horn which is dimensioned to be resonant and which is in forced engagement with at least one of the workpieces to be welded, said method comprising the steps of: establishing forceful contact between said horn and workpieces such that said workpieces are in engagement with one another at least along areas constituting a weld line to be formed;   energizing said electroacoustic transducer so as to resonate said horn with a desired motional amplitude;   maintaining said forceful contact between said horn and said one workpiece throughout said work cycle; and   varying said motional amplitude of said horn during said weld cycle in accordance with a desired motional amplitude profile.   
     
     
       3. The method of claim 2 wherein said step of varying said motional amplitude of said horn comprises energizing said electroacoustic transducer for a first portion of said weld cycle within a first range of power levels for preheating at least portions of said workpieces generally within said weld line, and then energizing said electroacoustic transducer for the remainder of said weld cycle within another range of power levels for heating both of said workpieces in the general area of said weld line to a temperature sufficient to effect welding of said workpieces to one another. 
     
     
       4. The method of claim 3 wherein said step of energizing said electroacoustic transducer during said first portion of said weld cycle involves gradually increasing said power level from a low level to a higher level within said first range of power levels so as to effect at least partially melting of said workpieces along said weld line. 
     
     
       5. The method of claim 3 wherein said step of energizing said electroacoustic transducer during said first portion of said weld cycle comprises gradually increasing the motional amplitude of said electroacoustic transducer from about 5% to about 80% of its full motional amplitude so as to preheat said portions of said workpieces. 
     
     
       6. The method of claim 3 wherein the motional amplitude of said electroacoustic transducer is gradually increased from about 10% to about 40% of its full motional amplitude. 
     
     
       7. A method of ultrasonically welding two thermoplastic workpieces together along a predetermined weld line during a weld cycle so as to reduce the formation of particulate weld material which may contaminate a product made from said workpieces or contained within said workpieces, one of said workpieces having an energy director on one of its surfaces to be welded to said other workpiece along said weld line, said method comprising the steps of: bringing said workpieces together with said energy director bearing against said other workpiece along said weld line to be formed;   providing an ultrasonic electroacoustic transducer for applying ultrasonic power to said one workpieces;   energizing said electroacoustic transducer for a first portion of said weld cycle at a first motional amplitude sufficient to preheat said energy director thereby to minimize shattering of said energy director; and   then energizing said electroacoustic transducer for the remainder of said weld cycle at another motional amplitude for the remainder of said weld cycle for heating said thermoplastic material of both of said workpieces along said weld line to a temperature sufficient to effect welding of said workpieces to one another.   
     
     
       8. The method of claim 7 wherein said step of energizing said electroacoustic transducer at said first motional amplitude involves gradually increasing said motional amplitude during said first portion of said weld cycle.